1. Field of the Invention
This invention relates to a pressure-sensitive copying paper using as a color former a pyridine-carboxylic acid lactone represented by the formula ##SPC3##
Or a mixture thereof, wherein R.sub.1 represents a hydrogen atom, a lower alkyl group or a benzyl group; R.sub.2 represents a lower alkyl group, a benzyl group or a substituted or unsubstituted phenyl group wherein the substituent is a lower alkyl group or a halogen atom; R.sub.3 represents a hydrogen atom, a lower alkyl group, a halogen atom or a phenyl group; and ##SPC4## represents ##SPC5##
Wherein R.sub.4 represents a hydrogen atom, a lower alkyl group, a lower alkoxy group, a halogen atom, an amino, mono-lower alkylamino, di-lower alkylamino, monobenzylamino, dibenzylamino, N-lower alkyl-N-benzylamino, anilino, N-lower alkylanilino or -NHCO-X group wherein X represents a lower alkyl, lower alkenyl or a substituted or unsubstituted styryl, phenyl or naphthyl group, the substituent being a lower alkyl, lower alkoxy, di-lower alkylamino, hydroxy or nitro group or a halogen atom, wherein the lower alkyl, alkoxy and alkenyl groups have 1 to 5 carbon atoms.
2. Description of the Prior Art
In general, pressure-sensitive copying paper comprises the combination of an upper sheet paper (or transfer sheet) having coated on the back surface thereof minute microcapsules containing dissolved therein an electron donative substantially colorless organic compound capable of undergoing color reaction, i.e., color former, and a lower sheet paper (or receiving sheet) having coated on the surface thereof a color developer. When these two coated surfaces are brought into contact with each other and a localized pressure is applied to the assembly by handwriting or typewriting, microcapsules located at the pressure-applied area rupture and the organic color former contained in the organic solvent comes into contact with the color developer to form color.
Pressure-sensitive copying paper systems comprising the aforesaid transfer sheet and a receiving sheet and an intermediate sheet are also known. In these systems the middle sheet is usually coated, on opposite surfaces, with a layer of microcapsules containing a color former solution and with a layer of a solid acid and a binder, respectively. Another type of pressure-sensitive copying system is a recording sheet which can be prepared by applying the above described microcapsules and the adsorbent solid acid on the same surface of a support.
As the color developer, there are active clay substances such as acid clay, attapulgite, zeolite, bentonite; solid organic acids such as succinic acid, tannic acid, benzoic acid; and acidic polymers such as phenol-formalin polymer, phenol-acetylene polymer, residual acid group-containing styrene-maleic anhydride polymer, salicylic acid-formalin polymer.
As the organic solvent for dissolving the color former, there are, such as ethylene glycol, chlorobenzenes, diphenyl chloride, diethyl phthalate, trioctyl phosphate, dibenzyl benzene, dibenzyl toluene, alkylnaphthalenes and naphthylalkyl alcohols.